Incandescent lamp.



l. LANGMUIR.

INCANDESCENT LAMP.

APPLICATION FILED SEPT. 4. 1913.

1 ,246, 1 1 8. Pat ented Nov. 13, 1917.

Fig. l.

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Witnesses: Inventor:

by I

Hls fittorne g.

' UNITED STATES PATENT oFFIcE.

IRVING LANGMUIB, OF SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

INCANIDESOENT LAMP.

Specification of Letters Patent.

Application filed September 4,, 1913. Serial No. 788,165.

To all whom it may concern:

Be it known that I, IRVING LANGMUIR, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork,have invented certam new and usefullmprovements in Incandescent Lamps,of which the following is a specification.

My invention relates to incandescent electric lamps and more articularlyto lamps having filaments of re ractory material such as tungsten.

In my prior Patent 1,180,159, issued A ril 18, 1916, I have disclosed alamp which as its filament so fashioned as to size, shape and materialand surrounded by an atmosphere of nitrogen or mercury vapor that thefilament can be run at a much higher temperature and at a higherefficiency than would otherwise be posible.

My present invention comprises certain improvements whereby the vapor ofa substance such as mercury may be conveniently and effectively createdand utilized in a lamp of this character.

The use of an atmosphere of mercury presents the marked advantage thatit operates in some way to protect the filament/from the effect of anywater vapor that may be present in the lamp. Since mercury vapor ismonatomic it is not dissociated even at the highest temperature attainedby an incandescent tungsten filament. It is a poor conductor of heat,and at suitable pressures it causes the rate of evaporation of atungsten filament to be much lower than the rate at which such a'filament evaporates in a vacuum or even in an atmosphere of inert gas.Mercury vapor at atmospheric pressure, for example, has a very greatefiect in preventing such evaporation.

According to my invention, I place in the lamp bulb a small quantity ofthe substance, mercury for example, to be vaporized by heat from thefilament, and I introduce into the lamp some suitable inertgas, such asnitrogen or hydrogen or a mixture thereof, which will absorb enough heatfrom the filament to prevent it attaining a dangerously high temperaturebefore the mercury vaporizes, and I construct the lamp in such a waythat the mercury vapor when produced displaces the nitrogen or otherinert gas, so that, except momentarily at starting, the filamentoperates in an atmosphere of the vapor of the mercury or similarmaterial.

For a better understanding of my invention, reference may be had to theaccompanying drawings in which,,for purposes of illustration, I haveshown some of the many different forms in which my invention may beembodied. Figure 1 is a view of one form of lamp embodying my invention,and Figs. 2, 3, 4 and 5 are views of modified forms of lamps embodyingmy invention.

In the particular form of lamp shown in Fig. 1, a filament 1, preferablyof drawn tungsten, is connected to and carried by comparatively stifiheavy leads 2, preferably made of tungsten or other highly refractorymetal. The filament must be either of relatively large cross-section,for example, 10 or 20 mils in diameter or larger, or if not of largecross-section, then it must be so fashioned, as by coiling into a closehelix, shaping into a tube either split or otherwise, as to give thesame effect with respect to exposed surface. This is for the reason, asI have found, that, within limits, a large cross-section filament losesheat by convection and conduction practically no faster than a filamentof small cross-section, but as its light radiating surface is muchgreater than that of the smaller filament, its efiicieucy as a lumiuantis therefore much higher. It is this factor as Well as the hightemperature whichthe filament can sustain without prohibitivevaporization under the conditions of operation which enables a highernet efficiency to be obtained than is possible if the same filament wereoperated in a vacuum.

Referring again to Fig. 1, the leads 2 are hermetically sealed, asindicated conventionally in the drawings, into the Walls of the lampbulb, usually made of material such as glass or quartz. Any suitableseal may be employed, the particular seal to be used formlng no part ofmy present invention. In the particular form of bulb shown the leads 2are sealed into the 'wall of an upper portion or condensing chamber 4which is connected through a constricted passage or neck 5 with the 10ver or bulb portion 6. This lower portion 6 is immediately adjacent thefilament 1 and constitutes the light transmitting portion of thebulb. Aquantity of material such as mercury 7 is placed in the bulb portion 6close enough to the filament 1 Patented Nov. 13, 1917. i

to be vaporized by heat from the filament. The bulb portion 6 is of sucha size and so proportioned that when the lamp is in operation its wallsare kept at such a temperature by the heat from the filament that themercury or other material will not condense on these walls, consequentlythe mercury vapor passes'through the constricted neck 5 into the upperor condensing chamber 4 and is there condensed. When the lamp is inoperation the mercury vapor may normally extend to about the level ofthe dotted line 8, the cooling and condensing action of the walls of thechamber 4 being sufiicient to condense practically all of the mercuryvapor before it rises any higher.

In some cases it ma be desirable to place a baflie or similar device 9adjacent the constricted portion or neck 5 in order to control the flowof mercury vapor from the lower bulb or chamber into the uppercondensing chamber, whereby it sweeps up into the upper chamber as asort of blast and carries with it any water vapor or foreign gas thatmay be liberated in the lower bulb. This bafile may assume manydifferent forms, one simple form being that shown in the drawing inwhich a disk or plate of glass is secured to the leads 2 in suchrelation to the neck 5 as to produce the desired effect on the flow ofmercury vapor.

As there is practically no mercury vapor around the filament when thelamp is cold, I avoid injury to the lamp as a result of running thefilament without the atmosphere of mercury vapor for the short period oftime between the turning on of the current and the evolution of themercury vapor by putting into the lamp, as I have heretofore mentioned,in addition to the mercury, an atmosphere which will surround thefilament whenever the mercury vapor does not do so, and which willprotect the filament until the appearance of the atmosphere of mercuryvapor at suitable pressure. I prefer to use for this purpose some inertgas like nitrogen which does not difi'use into the mercury vapor to anobjectionable extent, and does not attack the filament or the leads.Hydrogen may be mixed with the nitrogen because of its good heatconductivity. I prefer so to proportion the lamp that when it is innormal operation the contents are at about atmospheric pressure as ingeneral the higher the pressure of the mercury vapor the better theeificiency of the lamp. The pressure of nitrogen is in any event suchthat when current first flows through the filament the nitrogen willconduct heat away from the filament so rapidly that the filament doesnot reach a dangerous temperature while the mercury is being vaporizedto produce the proper atmosphere. In accordance with my invention Icause the nitrogen or other gas to move away from the neighborhood ofthe filament as quickly and as completely as pos sible after the lamp islighted, and thereafter run the filament in mercury vapor alone, so thatI am able to obtain much higher efficiencies and better results than arepossible where nitrogen or similar gas is in contact with the filamentall the time the lamp is lighted. The mercury vapor is approximatelyseven times as heavy as the nitrogen, and displaces the nitrogen,forcing it up away from the filament and into the upper chamber 4. Noneof the mercury vapor can condense upon the hot walls of the bulb portion6 as long as the lamp is lighted, but condensation does take place inthe upper or condensing chamber 4 to such an extent that the mercuryvapor forms a line of demarcation as, for example, at 8. The filamentthen runs at very high temperature in an atmosphere of mercury vapor atabout atmospheric pressure, or whatever pressure is selected as mostsuitable, while the nitrogen remains practically quiescent in the upperpart of the condensing chamber 4 and out of contact with the filamentuntil the lamp is turned off, whereupon the mercury vapor condenses, themercury collects in the bottom of the bulb portion 6, and the nitrogenagain fills the bulb portion 6 and surrounds the filament 1.

The nitrogen gas, in addition to its important function in preventinginjury to the filament when the lamp is started into operation, servesto equalize the pressure in the bulb against the cooling effects ofdrafts and against the changes of temperature of the external atmospherewith changes in the seasons as from summer to winter or the like. Ithas, in short, a sort of cushioning effect, the result of which is thatas the mercury vapor pressure rises the nitrogen is compressed and thusmore condensing surface, in the bulb 4 for example, is exposed as theline 8 rises, whereby increase in mercury pressure is checked. Theopposite effecfl occurs when the external conditions tend toward greatercooling of the bulb. The gas cushion has still another important effectin preventing arcing between the filament ends because if properlyproportioned, it prevents the pressure in the bulb from becoming, underany conditions, as low as to render arcing possible. Thus when the lampis cold and practically no vapor of mercury is present, the gas pressuremust be above the arcing point. This pressure is somewhat indefinite butnevertheless very considerable. The pressure should be not less thanseveral centimeters and preferably such as to give atmospheric pressureor thereabout when the lamp is running.

When the lamp is lighted, the bulb portion 6 is so hot that veryconsiderable amounts of water? vapor and occluded gases may be drivenout of its walls. If the mercury va- Eor were not present, the bulb 6would lacken very quickly, probably as a result of the action of thiswater vapor, but when the mercury is present the lam may run forhundreds of hours without b ackening. The mercury vapor seems to preventthe harmful effect of occluded gases or water vapor given out by thewalls of the bulb. I do not wish to advance or to be restricted to anyparticular theory as to the reason for the observed facts, but probablythe blast of mercury vapor keeps the water vapor away from the filament,and, the vapor rushing up through the constricted portion or neck 5 intothe condensing chamber 4, carries with it any deleterious gases or watervapor which may be present, so that such gases or vapors are depositedin the condensing chamber before they have an opportunity to exert anyharmful eifect upon the filament or light giving portion of the bulb. Itis also possible that in some way not clearly understood the mercuryvapor counteracts and nullifies the eflect of water vapor and otherdeleterious gases and vapors. At any rate, the evaporation of thefilament, the heat loss, and the harmful effect of the Water vapor areall much less when the filament is surrounded by mercury vapor than whenit is in contact with gas, such as nitrogen.

In the particular modification shown in Fig. 2 a substantiallycylindrical bulb 10 is divided into two communicating chambers orcompartments by a kind of baflie '01 partition 11 mounted in anysuitable way, as for example, on the leads 2. The operation of this lampis substantially the same as that shown in Fig. 1. When the lamp isstarted into operation the nitrogen surrounding the filament 1 absorbsheat and prevents overheating of the filament until the mercury vaporgenerated by the heat of the filament rises and displaces the nitrogen,driving it into the upper part of the bulb. As long as the lamp isrunning the filament is surrounded by an atmosphere of mercury vapor atsuitable pressure. When the lamp is turned off, the mercury condensesand the nitrogen again fills the whole bulb 10 and surrounds -thefilament 1 ready to perform its function when the lamp is again turnedon.

Fig. 3 shows a modification in which the lamp consists of two chambers12 and 13 in substantially the form of an hour glass. The leads 2 enterthe side of the bulb 13 and the constriction or neck 14 between thebulbs ermits the mercury vapor to force the nitrogen into the uppercondensing chamber 12 from which the condensed mercury falls back intothe bulb portion 13. As shown in this'figure the constriction or neckbetween the bulb and the condensing chamber of a lamp embodyingmy'invention can be so proportioned that there is no necessity for abaflle corresponding to the baflle 9 of the lamp shown in Fi 1.

Fig. 4 shows another form of lamp havmg a bulb substantially like thatshown in Fig. 3 and with the leads entering through the bottom of thebulb 13 instead of through the side. The filament is mounted in the bulb13 in a suitable way, as for example, on supports 15 made of tungsten orother refractory wire and secured to a central stem 16. The filament inthis figure, as in the other figures of the drawings, is shown as coiledinto a helix of small diameter and with the spires close together asalready pointed out. It is to be observed, however, that, wherever thefilament is sharply bent or is passed over supports as at 15 it is notcoiled. Certain structural features of the lam the filament an itssupport are described involving the contour of rial No. 154,606, filedMarch 13, 1917. The

mercury 7 surrounds the stem and is so related to the filament that itvaporizes when the lamp is turned on and the filament becomesincandescent.

Fig. 5 shows a modified form of lamp which is in general similar to thelamp shown in Fig. 1. The mercury vapor generated in the transparent orlight-giving portion 6 passes up through the neck 5 into the condensingchamber 4. In this particular modification I make special provision forreturning the condensed mercury through a passage separate from thatthrough which mercury vapor enters the condensing chamber. Oneparticular arrangement which may be used is that shown in the drawing,in which a mercury trap 17 permits the con densed' mercury to return tothe lower bulb portion 6 but prevents the passage of mercury vapor upinto the condensing chamber. By this arrangement the condensed mercuryis returned to a definite point in the bulb 6, while solid impuritiescarried by the condensed mercury float on the mercury in the trap 17 andare prevented from passing down into the lower bulb.

What I claim as new and desire to se cure by Letters Patent of theUnited States, is:

1. An incandescent lamp comprising a bulb,-a gas therein,non-condensable at ordinary temperatures, a material having in the vaporstate a poor heat conductivity and bein condensed at ordinarytemperatures, a lig t-giving body so located with respect to saidmaterial that said body will be surrounded by the vapor thereof to thesubstantial exclusion of said gas when the bulb is heated to theoperating temperature.

2. An incandescent lam elongated bulb, a gas therein, non-condensable atordinary temperature, a material having a poor heat conductivity in thevapor comprising an i state, and being condensed at ordinarytemperatures, a light-givin body located near one end of said bulb adacent said material, and being completely enveloped by the vapor of saidmaterial when at incandescence.

3. An incandescent lamp comprising a bulb having two portionscommunicating with each other through a constricted passage andcontaining two fluids differing in density the denser fluid being ofmaterially poorer heat conductivity than the other, said bulb beingshaped to permit one of said fluids to displace the other from one ofsaid portions of the bulb when the lamp is lighted, and a refractorymetal filament of large effective diameter mounted in one portion ofsaid bulb in a position to be surrounded by the heavier of said fluidswhile the lamp is lighted.

at. An incandescent lamp comprising. a bulb provided with two chamberscommunicating with each other through a constricted passage andcontaining two substantially non-diffusing atmospheres of differentdensitics, and a refractory metal filament of large effective diametermounted in one of said chambers in a position to be surrounded by thedenser atmosphere while the lamp is lighted.

5. An incandescent lamp comprising a bulb having communicating chambersand containing an inert gas, a condensable substance in the bulb adaptedto volatilize during operation of the lamp, and a refractory filament insaid bulb the space above the filament being constricted so that theblast of vapor thereby produced sweeps away from the vicinity of thefilament any water vapor or deleterious gases than may be freed duringoperation of the lamp.

6. An incandescentlamp comprising a bulb, a refractory metal filamenttherein of large effective diameter, a vaporizable material in said bulbadapted to be volatilized when the lamp is operated, and a gas cushionoperating at all times to prevent the variation in pressure due tovariation in the volatilization of said vaporizable material frombecoming such as would cause danger from arcing.

7. An incandescent lamp comprising a bulb, a refractory metal filamenttherein of large effective diameter, a vaporizable material in saidbulb, and a gas cushion operating so that the pressure in the lamp is attungsten filament of large effective diameter mounted in one of saidchambers, and a substance in the filament chamber which volatilizes whenthe lamp is lighted to produce a dense atmosphere which drives saidinert gas out of said chamber and away from the filament and completelysurrounds the filament while the lamp is lighted.

10. An incandescent lamp comprising a bulb having a light giving chamberand a condensing chamber, a filling of inert gas in said bulb suflicientin quantity to partially fill said condensing chamber at a predeterminedpressure, a body of mercury in said light giving chamber, and arefractory metaliilament of large effective diameter mounted in saidbulb in thermal relation to the mercury to volatilize the mercury andthereb produce a dense monatomic atmosphere of poor heat conductivitywhich at said predetermined pressure drives the inert gas into saidcondensing chamber.

11. An incandescent lamp comprising a bulb having a light giving portionand a condensing portion in communication therewith through aconstricted passage, a filling of inert gas in said bulb, a body ofmercury in said light-giving portion, and a filament of tungsten oflarge effective diameter mounted in said light giving portion inposition to vaporize said mercury and to heat said light giving portionto a temperature which prevents deposition of mercury thereon.

In witness whereof, I have hereunto set my hand this 30th day of August,1913.

IRVING LANGMUIR.

WVitnesses:

ALEX. F. MACDONALD, ALEXANDER D. LUNT.

